Respiratory systems provide breathable gas, such as oxygen, anesthetic gas and/or air directly to a patient's mouth, nose or airway to assist or facilitate breathing by the patient. A ventilator may be used as part of the respiratory system to drive the breathable gas to the patient through an inspiratory limb hose or conduit of a breathing circuit. The breathing circuit may also include an expiratory limb hose or conduit to carry expelled air and other gas(es) from the patient back to the ventilator.
It is typically desired to warm and impart humidity to the breathable gas before it is provided to the patient. For that purpose, many respiratory systems include a humidification system including a heater unit and a disposable water chamber adapted to be heated by the heater unit. The heater unit supports a hot plate heater, which may be comprised of one or more heating elements and a metal plate defining a hot plate. A wall of the chamber, such as the bottom surface of the chamber, is thermally conductive. The chamber is removably supported on the heater unit with the thermally conductive surface in thermal contact with the hot plate of the heater unit to thus heat the water in the chamber. The chamber may be manually refillable, or there may be a water source to selectively fill the chamber as it empties. The breathable gas is coupled to the chamber and is passed through the chamber to be heated and humidified. Examples of heater units, chambers and vented water supplies are shown in U.S. Pat. Nos. 6,988,497 and 5,943,473; and co-pending U.S. patent application Ser. Nos. 11/469,086 and 11/469,113, both filed Aug. 31, 2006.
The inspiratory limb carries the heated and humidified gas to the patient and the expiratory limb, if present, carries exhaled air and possibly other gases from the patient. The inspiratory limb and the expiratory limb may each be provided with a heater circuit to add heat to the gas passing through the limb. The heater circuit may be in the form of one or more elongated, and possibly coiled, heater wires running along the limb, such as through the interior of the limb. An example of a breathing circuit with heated limbs is shown in U.S. Pat. No. 6,078,770. The heater unit typically houses the necessary electrical and electronic components to regulate the temperature of the hot plate, as well as the heater circuit(s) of the inspiratory and/or expiratory limbs of the breathing circuit. To that end, the temperature of the gas passing through the breathing circuit may be monitored at various locations, two examples of which are at the outlet of the chamber (i.e., the inlet to the inspiratory limb) and/or at the outlet of the inspiratory limb (i.e., at the patient). The temperature of the hot plate may also be monitored. The temperature readings obtained are utilized by the heater unit for purposes of regulating the various heating components.
With respect to the heating circuits, the heater unit regulates the power thereto in relation to the resistance of the heating circuit based on the watt density and length of the wires employed in the heating circuit, for example. There are many types of breathing circuits that might be employed, depending on the nature of the respiratory system and its application. By way of example, some breathing circuits have only an inspiratory limb; some have both inspiratory and expiratory limbs. In some situations, one or both of the limbs has a heater circuit. Moreover, the nature of the heating circuit and the limbs may differ depending upon whether the breathing circuit is for adult, pediatric or neonatal application. In each situation, the heater unit and breathing circuit have to properly matched, so that the heater unit is set up appropriately depending upon whether or not a respective heater circuit is present or to be used, and if so, for the specifics of that heater circuit, such as the resistance thereof. The user or operator of the heater unit must thus take care to select a proper breathing circuit, to properly connect the heater circuit(s) to the heater unit, and to properly set up the heater unit for that breathing circuit. Failure to properly set up or connect to the heater circuit, or using an incorrectly matched breathing circuit, can lead to serious adverse consequences. Accordingly, additional levels of protection are desirable to ensure proper selection, connection and set up of breathing circuits to heater units to avoid the adverse consequences of an incorrectly matched or connected breathing circuit.